In the GNOME bugzilla, there is an ongoing discussion about whether or not to include a patch into the default GNOME installation which would enable GNOME to (optionally) have a global application menubar, similar to that of the Mac OS and KDE (in the latter it is optional and off by default). Installation instructions and .deb packages, as well as a 60-page (and counting) discussion of the patch, are available on the UbuntuForums. Read on for a poll on this issue.

Firefox does noy use PURE GTK2 to draw its interface. It uses XUL which uses GTK2 look, this makes Firefox unusable with Mac style GTK2 menubar [While menu disappears from GTK2 apps and shows as the Mac menu, Firefox menu is still there untouched and Mac menu is empty], I wonder how do they resolve this.

.. and yes, add that functionality to Gnome, by default off of course, great feature not only for Mac OS X incomers but also for everybody that wants to try something new.